Mind-Blowing Quantum Physics in 5 Minutes
A neat party trick with a coin to impress your friends.
While reading about quantum physics for the first time, I began compacting as much of the complicated math, equations and theories into as simple of an understanding as possible. I wanted to create a neat little package of knowledge to take away from what I had learned so that I could say to some degree: “I understand quantum physics.”
Not only did this process help me internalize and retain this knowledge, but to my great surprise, it became a delightful little presentation I could explain from memory. With a group of people willing to listen for five minutes — such as at a bar as the second round of drinks arrive — this little story, told while playfully flipping a coin in the air, became a big hit.
Let’s begin…
Preamble: A Departure From What We Know
Quantum physics is the study matter and energy at the fundamental, subatomic level. It differs greatly from what we call “classical physics” or “Newtonian physics,” that which was pioneered by Sir Isaac Newton. At the subatomic level, things behave much, much differently, and as we’ll see, this has some pretty incredible implications about the very fabric of reality.
Much of what became the theory of quantum physics came from studying electrons, the tiny particles that orbit the nucleus of an atom. Through the lens of classical physics, we might think of electrons orbiting the nucleus in the way that planets orbit the sun, and therefore, we might be able to predict their position, velocity, rotation and other properties according to our knowledge of said physics.
As it turns out, we’d be wrong. You see, electrons are like flipping a coin.
The Wave Function
Imagine a coin with two faces, heads and tails. It can be heads, or it can be tails. If I want to know which one it is, I simply look at it and see either George Washington or a bald eagle.
Now flick that coin into the air, and as it floats upward, spinning end over end, stay in that moment. Is the coin heads or tails? You might say, “It’s neither.”
Not quite…
You might also say, “We don’t know yet; it hasn’t landed.”
This is a bit closer to the quantum truth. But in reality, the best answer at this point is simply: “Both.”
In quantum physics terms, this would be called “a superposition of all possible states.” And if you look closely at the coin tumbling end over end, you don’t really see heads or tails, or even something coin-shaped anymore. You see a silver blur, a translucent, spherical cloud.
Electrons behave the same way in that their “orbit” around the nucleus of an atom does not have definite position, but rather exists in an electron cloud representing a superposition of all possible positions. If we were to make a graph of these possible positions, we’d see a wave-shaped distribution pattern that can be expressed by a function, which scientists call “the wave function.”
Pretty interesting, but so what?
The Measurement Problem
Before continuing, there’s one little concept to discuss first.
Our coin is spinning through the air. It’s still in a super position of its two possible states, heads or tails, just like every electron in the universe. But eventually, we’re going to catch it in our hand, and then we know without a shadow of a doubt that we are seeing either heads or tails.
The same thing happens with electrons when scientists attempt to measure their position, velocity or spin. There is no way to measure an electron without somehow interacting with it, just like grabbing the coin out of the air.
You might think scientists could just take a photo of the electron without touching it, right? But no. Just like taking a photo in the dark, a camera has to beam light onto its subject. With subatomic particles, this means beaming a photon of light at the electron and waiting for it to bounce to the camera lens. This makes contact with the electron and thereby forces into providing the position we want from it. And in just the same way that we are forcing the coin to become one of its two possible states at random, so, too, do scientists force a position state from the electron that falls somewhere on its wave function.
Still with me? Great.
Collapsing the Wave Function
Our coin is still spinning through the air in the super position of both states, and we know now that in order to “measure” the coin for a value of heads or tails, we have to grab it out of the air and use our hand to flatten it into one of the two possible states.
Let’s say it’s heads.
And as long as it sits in my hand with George Washington’s profile staring up at us, it will remain heads.
Definitely heads, and not tails.
Until I flip it again, right?
For coins, yes. But for electrons, no.
When a scientist measures an electron’s position, the interaction of the measurement forces that electron into a position chosen randomly from all possible positions. This is permanent. If that same scientist measures another electron, that electron will likewise be forced into some other random position from its range of possible positions.
But if a scientist measures the same electron twice, the second measurement will always be the same as the first. The reason is that the interaction of the measurement has “collapsed the wave function.” This is what the early pioneers of quantum physics (Albert Einstein among them) discovered. They were able to observe this phenomenon consistently and to create all kinds of complicated math that proves that these are the laws of physics at the atomic scale, and from that, a lot of cool scientific applications were possible.
But what does it really mean?
The Many Worlds Theory
Remember when we first flipped that coin and wondered, “Is it heads or tails?” We said the answer is “both,” but how can that be true once we grab it from the air and force it to be forever heads or forever tails?
The same question applies for an electron: How can it be in more than one position after we’ve measured it and collapsed the wave function? One outcome has taken place and the other(s) have not, right?
Maybe not.
When we interact with an electron by measuring it, we become “entangled” with it. When I grab that coin out of the air, it and I are now entangled, and according to the many worlds theory of quantum physics, this means that reality has just split into two separate dimensions. In one dimension, there is me holding a coin that is heads, and in the other dimension, there’s me holding a coin that is tails.
Both outcomes have occurred.
When I look at the coin and see heads, I have not learned the definitive and mutually exclusive outcome of the coin flip. Instead, I have merely learned in which dimension I now reside.
Pretty freaky, but simple enough, right?
A coin only has two states: heads or tails. In quantum physics, this is called a “qubit,” which is a simple mechanism for examining quantum theory in the abstract (and has some real applications for quantum computing). But a real electron does not have only two states; it has an exponential number of possible positions, not to mention states that are combinations of position, velocity, spin and other properties.
So when a scientist measures an electron, collapses its wave function and becomes entangled with it, does it — what? Split into an exponentially infinite number of dimensions?
Yes! That’s the “many” part of the many worlds theory.
The fabric of reality is therefore densely packed with alternate dimensions created whenever particles throughout the history of time have become entangled. As time marches forward, reality becomes ever denser with dimensions representing every possible outcome that could have (and in every case, always did) ever happen.
What we experience as human beings is one infinitely small slice from the whole of reality, which includes nearly infinite copies of ourselves having experienced infinitely different outcomes in our lives. What we experience does not tell us what has happened or what has not happened, it just tells us in which of these innumerable dimensions we now reside.
How’s your mind? Blown?
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